Adaptive droving behavior observed in the fiddler crab Uca vocans vocans

Droving is conspicuous in Uca vocans vocans in summer. The crabs burrowing on the upper habitat have a higher tendency to wander compared to the ones burrowing on the lower habitat. Most of the wandering crabs captured on the low tide levels are relatively large and male. Larger crabs and males prefer to burrow on the upper zones of U. vocans habitat, but the smaller ones and females prefer the lower habitat. The upper level of the U. vocans habitat has relatively low N-content compared to the water's edge. Therefore droving is advantageous in crabs that have burrows on the upper level. Female and smaller resident crabs have faster feeding motions than male and larger ones, and can satisfy their feeding demands more rapidly. Therefore, for males and larger crabs it is advantageous to move away from the burrow area and forage in areas of higher food content near the low tide level where the number of feeding motions increases.     

Some aspects of the ecology of the echiuran worm Bonellia viridis and associated infauna

In inshore waters around Malta, Bonellia viridis inhabit burrows with multiple exits in calcareous rocks, and are most abundant in areas bordering Posidonia oceanica meadows. The associated epiflora and fauna are typical of the Mediterranean hard-substrate infralittoral zone. The larger infaunal species associated with B. viridis include a poriferan, Cliona sp.; an unidentified nemertean worm; various polychaetes; the sipunculans Phascolosoma granulatum and Aspidosiphon muelleri; two species of molluscs-Lithophaga lithophaga and Lepidopleurus cajetanus; 8 species of decapod crustaceans; and the teleost Gobius geniporus. Four types of burrows are found in rocks containing B. viridis. The larger burrows (referred to herein as UBA burrows) contain 3 main species-the decapods Upogebia deltaura and Alpheus dentipes and B. viridis itself. Experimental evidence suggests that U. deltaura excavates the UBA burrows mechanically, although B. viridis may secondarily modify them by secretion of an acidic mucus and gentle mechanical action. There is a definite community of organisms living as commensals in the burrow of U. deltaura. The assemblage of organisms bears a striking parallelism to the assemblages inhabiting the burrows of species of Upogebia, Callianassa and the echiuran Urechis caupo of the Pacific coast of N. America. A food web for the UBA burrow community is suggested.     

Interspecific attractiveness of structures built by courting male fiddler crabs: experimental evidence of a sensory trap

Male fiddler crabs Uca musica sometimes build sand hoods and male Uca beebei sometimes build mud pillars next to their burrows to which they attract females for mating. Mate-searching females preferentially approach these structures and subsequently mate with structure builders. Here we show that the preference for structures is not species-specific and argue that it may not have evolved for mate choice. When not near burrows, many species of fiddler crabs approach and temporarily hide near objects, suggesting that hoods and pillars may attract females because they elicit this general predator-avoidance behavior. To test this sensory trap hypothesis we individually released female U. musica, U. beebei and Uca stenodactylus, a non-builder, in the center of a circular array of empty burrows to which we added hoods and pillars and then moved a model predator toward the females. All species ran to structures to escape the predator and the two builders preferred hoods. Next, we put hood replicas on male U. beebei burrows and pillar replicas on male U. musica burrows. When courted, females of both species preferentially approached hoods as they did when chased with a predator. However, males of both species with hoods did not have higher mating rates than males with pillars perhaps because hoods block more of a male's visual field so he sees and courts fewer females. Sexual selection may often favor male signals that attract females because they facilitate general orientation or navigation mechanisms that reduce predation risk in many contexts, including during mate search.     

Burrow structure, burrowing and feeding behaviour of Corallianassa longiventris and Pestarella tyrrhena (Crustacea, Thalassinidea, Callianassidae)

The behaviour of the Caribbean Corallianassa longiventris and the Mediterranean Pestarella tyrrhena, two burrowing thalassinideans, was studied in situ and in laboratory aquaria. Burrows of C. longiventris were closed most of the time; they consist of a deep U (down to 1.5 m) with upper and deeper chambers, some of them filled with macrophyte debris. The burrows of P. tyrrhena reached down to a maximum depth of 54 cm and consisted of a shallow U with a mound and a funnel, and a spiral shaft from which several, often debris-filled chambers branched off. The appearance of C. longiventris at the sediment surface to collect debris is strongly triggered by wave swell or odours from plant and animal juices; its burrows are opened within 10 min. The surface activity of P. tyrrhena was relatively less frequent and less predictable. Inside the burrows, both species exhibited different patterns of time allocated to 25 defined behavioural states. After being offered seagrass debris, P. tyrrhena spent relatively less time manipulating this debris, but it handled sediment more often than C. longiventris. During frequent mining events, both species showed sediment-sorting behaviour, which brought a parcel of sediment in close contact with the mouthparts; some of this sediment may be ingested because the fecal rods produced by both shrimps contain very fine sediment particles. Seagrass debris is irregularly tended by P. tyrrhena after its introduction into the chambers. Such material ultimately becomes buried. Corallianassa longiventris frequently returns to its debris chambers to pick up pieces of seagrass, which are subsequently cut with the chelae or ripped with the third maxilliped and then transported to another empty chamber nearby. Pieces become smaller with time and show curved cutting edges and bite marks. After 100 to 140 days, 2 to 6 g(dw) seagrass debris are consumed in this manner by individuals of this species. The debris-related behaviour of P. tyrrhena probably enriches the sediment around the burrow for stochastic encounters during later mining events. Such an indirect benefit may also be effective on a population level because other individuals may also encounter this buried nutrient source. Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

New Genetic Approach to Detecting Individuals of Rare and Endangered Species

Abstract: Many rare and endangered species are difficult to locate, observe, and study. Consequently, many individuals, breeding pairs, and even populations of such species could remain undetected. Genetic markers can potentially be used to detect the existence of undiscovered individuals and populations, and we propose a method to do so that requires 3 conditions. First, sampling of the known population(s) of the target species must be comprehensive. Second, the species must display a reasonable level of philopatry and genetic structuring. Third, individuals must be able to be caught outside of breeding locations (e.g., at courtship or feeding areas, in flight), and the level of recapture must be reasonably high. We applied our method to the Chatham Island Taiko (Pterodroma magentae), one of the world's most endangered seabirds. We sequenced the Taiko mitochondrial cytochrome b gene and both copies of a fragment of the duplicated domain I of the control region. Twenty‐one haplotypes were revealed, including 4 (19%) not found in birds at known burrows. These results suggest there are more burrow groups yet to be located. The species is a pelagic gadfly petrel that inhabits land only in the breeding season during which it is nocturnal and nests in burrows. Taiko burrows are situated in dense forest in a remote area of Chatham Island, and are consequently difficult to locate and study. It is important that all Taiko burrows be discovered to enable monitoring and protection of the birds from exotic predators.     

Some direct observations on the ecology and behaviour of the Norway lobster Nephrops norvegicus

A detailed investigation of a small area of sea bed occupied by the Norway lobster Nephrops norvegicus (L.) was carried out by diving and television observations at depths of 30 m in Loch Torridon, Scotland. The density of burrows was 1/2 m², but only a proportion of these were occupied by N. norvegicus. Although about 70% of the larger burrows were occupied by N. norvegicus, giving a density of 1 lobster/8 m², very few juveniles (carapace length less than 30 mm) were found in the area. Many of the small burrows were occupied by the gobiid fish Lesueurigobius friesii (Collett). There was evidence that N. norvegicus frequently change their burrows, and fighting for burrows was observed. N. norvegicus remain within their burrows during the day, emerge around sunset to forage for food during the night, and then return to their burrows at dawn. This, and other aspects of their burrowing behaviour, have a marked effect on the commercial trawl catches of N. norvegicus which show large seasonal and diurnal variations in size and sex composition.     

Feeding ecology of the mangrove crab <Emphasis Type="Italic">Ucides cordatus</Emphasis> (Ocypodidae): food choice,food quality and assimilation efficiency

Food preferences, consumption rates and dietary assimilation related to food quality were investigated for the large semi-terrestrial and litter-consuming mangrove crab Ucides cordatus cordatus (Ocypodidae, L. 1763) in northern Brazil. Stomach contents were composed of mangrove leaves (61.2%), unidentified plant material and detritus (28.0%), roots (4.9%), sediment (3.3%), bark (2.5%), and animal material (0.1%). U. cordatus prefers Rhizophora mangle over Avicennia germinans leaves despite a higher nitrogen content, lower carbon to nitrogen (C/N) ratio and lower tannin content of the latter. Also, assimilation rates for senescent R. mangle leaves (C: 79.3%, N: 45.4%) were higher than for A. germinans leaves (C: 40.6%, N: 9.1%). Faeces composition indicates that A. germinans leaves were more difficult to masticate and digest mechanically. The leaf-ageing hypothesis, according to which crabs let leaves age in burrows to gain a more palatable and nutritive food, was rejected for U. cordatus since N content, C/N ratio and the abundance of microorganisms did not differ significantly between senescent leaves and leaves taken from burrows. The low microbial biomass on leaf surfaces and in the sediment indicates its minor importance for the nutrition of U. cordatus. It is concluded that high ingestion and assimilation rates of a R. mangle diet together with the consumption of algae allow for a high intake of C, N, and energy. The data suggest that the digestibility of mangrove leaves by U. cordatus is not hampered by tannins. This may have provided a competitive advantage over other leaf-consuming invertebrates unable to digest mangrove litter with high tannin concentrations. Due to the large stock biomass of U. cordatus in the study area, a great amount of finely fragmented faeces is produced (about 7.1 ton dry matter ha⁻¹ year⁻¹ in a R. mangle forest) which is enriched in C, N and bacterial biomass compared to the sediment. The decomposition of mangrove litter, and thus nutrient and energy transfer into the sediment, is greatly enhanced due to litter processing by U. cordatus.     

Natal philopatry in bannertailed kangaroo rats

Summary I describe prolonged retention of offspring in natal home ranges, or natal philopatry, in the bannertailed kangaroo rat Dipodomys spectabilis. Though weaning occurs at about one month of age, offspring shared natal burrows with their mothers for three to seven months, and 39% of surviving offspring remained within natal home ranges through reproductive maturity. Males as well as females were philopatric. Data on the availability of burrows and on patterns of resettlement suggest that natal philopatry in this species may be a means of providing juveniles with access to essential resources, in this case food caches and large complex burrow systems, that are not readily available outside natal home ranges.     

Reproductive biology of a filter-feeding amphipod, Leptocheirus pinguis , with extended parental care

Leptocheirus pinguis (Stimpson, 1853) is a widely distributed, abundant, endobenthic amphipod that engages in extended parental care, i.e. females host their juveniles in their burrows for extended time periods. I examined reproduction and population biology of L. pinguis at mean low water (MLW) in muddy sediment in Lowes Cove, Maine, USA. Cores around individual burrows were taken monthly in 1994 and 1995, and four seasonal samples were taken at different tidal heights. During the major reproductive periods in spring/early summer and in the fall, females produced several consecutive broods and hosted growing offspring in their burrows. Juveniles remained in their mothers' burrows until they reached a length of 5 mm (approximately one-third adult size) or more. At the study site, the majority of amphipods in individual burrows were adult females. Following the main reproductive periods, subadult individuals were found in their own burrows, but densities did not increase following the reproductive period in spring/early summer 1994, probably because large numbers of L. pinguis emigrated via the water column between June and December. L. pinguis is an annual species. Many members of the cohort born in spring/early summer start reproducing in the fall, and survive until the following spring when they produce several broods. Members of the cohort born in the fall start reproducing the following spring and also produce several consecutive broods. Both the spring/early summer and fall cohorts die off after the major reproductive period in the following spring/early summer. High standing stocks of microphytobenthos occur in soft-bottoms at MLW, and I conclude that L. pinguis can engage in extended parental care there because its food is abundant year-round. The limited expandability and low stability of burrows in soft-bottoms at MLW do not permit long persistence of parent–offspring groups in L.␣pinguis. Received: 27 March 1997 / Accepted: 30 July 1997     

Temporal constraints and female preference for burrow width in the fiddler crab, <Emphasis Type="Italic">Uca mjoebergi</Emphasis>

We studied sampling behaviour and mate choice in the fiddler crab Uca mjoebergi. Once a female selects a mate, she copulates in his burrow and remains there until releasing her aquatic larvae. U. mjoebergi occurs in habitats that are inundated only by the highest amplitude spring tides. Females can only release their larvae during these tides, and release before or after will result in complete failure of reproductive effort. Matings occur over a 5-day period near the end of neap tides. Our results suggest that within the mating period, females adjust their larval developmental rates by selecting specific burrows in which to incubate their clutches. We found that at the start of the mating period, females chose larger males as mates. Since male size was positively correlated to burrow width, females were selecting wide burrows and effectively incubating at lower temperatures. This would slow down the developmental rates of larvae. In contrast, females that mated late in the mating period selectively chose small males. By incubating in narrower, warmer burrows, these females may increase the developmental rates of larvae. We propose that females are selecting burrows to influence incubation rate and ensure timely release of their larvae. Female U. mjoebergi appear to adjust their preference for the direct benefits of mate choice to increase their reproductive success.     

Biparental investment and reproductive success in a subsocial desert beetle: the role of maternal effort

Parastizopus armaticeps is a nocturnal subsocial detritivorous desert tenebrionid that produces very few offspring per brood. The two environmental factors that constrain reproduction, rapid sand desiccation rate and food scarcity, are countered by biparental effort. Males dig and extend breeding burrows, maintaining their moisture level; females forage on the surface at night for high-quality detritus, the larval food. This was shown to be a scarce and unpredictable resource for which there is high competition. When food was supplemented in a field experiment, offspring number and survivorship doubled and burrow failure due to desiccation dropped from approximately half, the typical failure rate for unsupplemented burrows, to zero. Food supplementation did not, however, increase larval foodstore size and there was no difference in the size of the offspring produced. Supplemented females reallocated their time, foraging less and digging more with the male. This change in maternal behaviour patterns resulted in deeper burrows which remained moist longer, thus extending the larval production period. Female foraging efficiency, particularly food retrieval speed, determined how much time females could allocate to digging, consequently increasing the reproductive success of the pair. Burrow depth and sand moisture level at the burrow base were the major correlates of reproductive success, but the scarcity and unpredictability of high-quality food on the surface and the competition for this resource influenced the number of offspring indirectly through their effect on female behaviour. Received: 29 November 1996 / Accepted after revision: 7 December 1997     

Factors affecting the burrowing behaviour of Helice tridens (Grapsidae) and Macrophthalmus japonicus (Ocypodidae) in an estuary of northeast Japan

Helice tridens (De Haan) (Grapsidae) and Macrophthalmus japonicus (De Haan) (Ocypodidae) build separate burrows in reed marshes and muddy tidal flats, respectively, in the brackish-water estuaries of northeast Japan (38°11N, 141°48E). Habitat segregation between burrows of these two species was analysed by comparing the density of burrows of both species in their natural habitats, and on tidal flats subjected to various types of artificial treatment, in the summer of 1981 and 1982. Baskets, containing many stones, were placed on the ground in the reed marsh, tidal flat and creek and attracted many individuals of H. tridens, but not M. japonicus. When stones were placed on an area of tidal flat, H. tridens frequently formed burrows at the border between the stones and mud, suggesting that burrowing of H. tridens was related to the presence of solid substances lying on the ground, such as stones and shoots of the reed Phragmites australis (Cav.) Trin. In closed systems on the tidal flat and reed marsh, H. tridens and M. japonicus were able to construct burrows in both substrata regardless of high or low frequency. Moreover, it was recognized that H. tridens prevented the burrowing of M. japonicus in these closed systems. These results suggested that habitat segregation between H. tridens and M. japonicus burrows was caused primarily by an exclusive interaction between individuals of these two species.     

Meiofaunal thiobios and “the Arenicola negation”: Case not proven

It has been alleged recently that the distribution of meiofauna around Arenicola burrows disproves the existence of a specifically anaerobic marine meiofauna. Critical appraisal of the evidence on which this denial was based shows that the conclusion was untenable. It may have arisen mistakenly from inadequate sampling of the burrow micro habitats, from lack of complementary data on burrow wall oxygen regime and from prejudgement (by denying the possibility of primary anaerobiosis) of the reasons why species held to be anaerobic by other authors occur in proximity to oxic conditions. These points and some new data on Arenicola burrow oxygenation are discussed. It is shown that at present the evidence from meiofaunal distribution around Arenicola burrows may be taken as much in favour of thiobiotic theories as against them.     

Small-scale spatial and temporal interactions among benthic crustaceans and one fish species in the Bay of Biscay

In the summer of 2004, a video survey was carried out in the northern part of the central mud bank (Grande Vasière) of the Bay of Biscay to study the small scale relationship between the dominant crustacean megafauna Nephrops norvegicus, Munida rugosa and Goneplax rhomboides and juvenile hake (Merluccius merluccius). Using a towed body, high-resolution videos were recorded in six sampling sites. Statistical modelling using generalised additive models (GAM) revealed variations in activity patterns for two species. More N. norvegicus were observed outside their burrows at dawn and somewhat at dusk (no observations during night) while G. rhomboides was less observed in the morning. In addition, reduced spatial overlap between G. rhomboides and N. norvegicus suggested reduced competition for food but also space as both are burrowing species. The observed temporal and spatial activity patterns may contribute to regulating assemblage structure as competing species may be actively foraging at different times and locations thus reducing direct competition.     

Biology of the conger eel Conger oceanicus in the Mid-Atlantic Bight

In the Mid-Atlantic Bight, conger eels (Conger oceanicus) occur from the coastal portions of estuaries to the edge of the continental shelf. In deeper waters they occupy burrows of the tilefish (Lopholatilus chamaeleonticeps). Between 1972 and 1974 we examined the stomachs and intestines of conger eels from inshore New Jersey (USA) waters (n=35, with a total length: TL of 21 to 49 cm) and between 1980 and 1983 offshore (n=295, 50 to 125 cm TL)_collections. Eels from both areas fed primarily on decapod crustaceans and fish. The specific identity of prey items within these groups generally differed from inshore to offshore areas, probably reflecting the differences in prey availability. Foods of specimens collected offshore varied with size: smaller eels (<80 cm TL) fed most heavily on decapod crustaceans, whereas larger eels (>80 cm) consumed more fishes. The presence of some nocturnally active prey items in the gut, primarily the eel Lepophidium cervinum, suggests that conger eels are nocturnal feeders. This is supported by in situ observations that conger eels are present in some tilefish burrows during the day and are presumably out of burrows and foraging at night.     

A comparative study of feeding and growth in two coexisting species of carnivorous gastropods

The effects of variable food supply on growth rate and feeding behaviour in two coexisting intertidal gastropods were examined through field and laboratory experiments involving mark and recapture procedures, growth experiments under controlled food supply and video observations of feeding. All cohorts of both Japeuthria species grew most in summer, with the highest growth rate being achieved by the youngest cohort of both sexes. In contrast, almost all cohorts (except the youngest one) showed zero to negative growth in winter. The growth rates of Japeuthria species clearly varied depending on feeding frequencies and the initial size of individuals. Females of both species had a significantly higher growth rate than males, though the difference became less marked with decreasing food supply. The total time spent on feeding and the length of the first feeding bout generally increased as the duration of the interval between meals was increased across treatments. From both the field growth experiment and the observations of feeding behaviour it is clear that J. ferrea had a higher frequency of feeding than J. cingulata in the field; 1- to 3-d intervals of feeding frequency in the former and 3- to 6-d intervals in the latter. Most notably, the two species showed a reversal in growth rates with changing conditions of food supply. When food was relatively abundant J. ferrea achieved better growth than J. cingulata, but J. cingulata grew better than J. ferrea under low food supply. In view of the fact that J. ferrea seems to be competitively superior to J. cingulata under normal levels, the present observation that J. cingulata can perform better than J. ferrea when food availability is low gives an important advantage to the latter in terms of its coexistence with the former. Received: 9 March 1999 / Accepted: 8 October 1999     

Observations on the burrows and burrowing behaviour of two mud-dwelling decapod crustaceans,Nephrops norvegicus and Goneplax rhomboides

The burrows of the Norway lobster Nephrops norvegicus (L.) and of the crab Goneplax rhomboides (L.) were studied in Loch Torridon, Scotland. Polyester resin casts of burrows in the sea were made by divers to reveal their subsurface form. Tunnels made by N. norvegicus were usually simple, with two or more openings on the mud surface, and penetrated to a depth of about 30 cm. G. rhomboides burrows did not descend more than about 15 cm beneath the surface, but were usually more complex than the lobster burrows and had several openings. The methods of burrow construction used by the two crustaceans are described from aquarium observations. Neither N. norvegicus nor G. rhomboides show obvious morphological adaptations for burrowing, and it is suggested that the fossorial habit was adopted very early by decapods. The burrows of N. norvegicus do not seem to have assumed any functions in addition to the original one of providing refuge from predators. There is not sufficient known of the biology of the crab to indicate whether the same is true in its case.     

Predation risk and foraging behavior of the hoary marmot in Alaska

Summary I observed hoary marmots for three field seasons to determine how the distribution of food and the risk of predation influenced marmots' foraging behavior. I quantified the amount of time Marmota caligata foraged in different patches of alpine meadows and assessed the distribution and abundance of vegetation eaten by marmots in these meadows. Because marmots dig burrows and run to them when attacked by predators, marmot-toburrow distance provided an index of predation risk that could be specified for different meadow patches.Patch use correlated positively with food abundance and negatively with predation risk. However, these significant relationships disappeared when partial correlations were calculated because food abundance and risk were intercorrelated. Using multiple regression, 77.0% of the variance in patch use was explained by a combination of food abundance, refuge burrow density, and a patch's distance from the talus where sleeping burrows were located. Variations in vigilance behavior (look-ups to search for predators while feeding) according to marmots' ages, the presence of other conspecifics, and animals' proximity to their sleeping burrows all indicated that predation risk influenced foraging.In a forage-manipulation experiment, the use of forage-enhanced patches increased six-fold, verifying directly the role of food availability on patch used. Concomitant with increased feeding, however, was the intense construction of refuge burrows in experimental patches that presumably reduced the risk of feeding. Thus, I suggest that food and predation risk jointly influence patch use by hoary marmots and that both factors must be considered when modeling the foraging behavior of species that can be predator and prey simultaneously.     

Adaptive behaviour of chironomid larvae (Chironomus riparius) in response to chemical stimuli from predators and resource density

Chemical-mediated effects of predatory fish on chironomid larvae behaviour have been ignored so far. Sediment-dwelling chironomid larvae inhabit protective burrows from which they extend their bodies only to feed on deposited detritus and microalgae from the surrounding sediment. Here, we performed factorial laboratory experiments to study whether fish-borne chemical cues (kairomones) are responsible for behavioural trait changes of chironomid larvae, and whether chironomid larvae are able to assess the densities of fish predators and food resources and the trade-off between them. We exposed naïve Chironomus riparius larvae to the chemical presence of zero, one, and ten predator fish (Rutilus rutilus) and offered two resource levels (low food, high food) for each treatment. Kairomones induced significant inherent behavioural trait changes in chironomid larvae. During the first 120 min after exposing chironomids to fish-conditioned water, we found a significant increase in digging activity with increasing predator density. After 3 days of exposure, the deepest chironomid burrows were found in treatments with the highest predator density. Chironomid larvae were significantly able to adjust their foraging behaviour to different predator densities and food concentrations and trade off between them; that is, when fish predators were more abundant or when more food resources were available, the foraging activities of larvae were significantly reduced. Our data suggest that chemically mediated trait changes (burrowing and foraging behaviour) may cascade through the littoral food web.     

Microbial reaction rates and bacterial communities in sediment surrounding burrows of two nereidid polychaetes (Nereis diversicolor and N. virens)

The effects of infaunal mode of life on sediment properties, microbial reaction rates, as well as abundance and composition of bacterial communities were studied in sediment surrounding burrows (mucus lining, oxidised wall, ambient anoxic and surface sediment) of two closely related, but behaviourally different, nereidid polychaete worms: the facultative suspension-feeder Nereis (Hediste) diversicolor and the obligate deposit-feeder Nereis (Neanthes) virens. Burrow sediment of the two species was collected from two adjacent (50 m distance) shallow sandy locations (Kertinge Nor, Denmark). The burrow lining and wall of both polychaete species were enriched in organic matter originating from mucous secretions by the inhabitants and phytoplankton trapped through irrigation. This was more evident for N. diversicolor that shows a significantly higher irrigation rate than N. virens. Both the organic matter mineralisation rates (based on anaerobic incubations) and bacterial abundance were higher along the burrow linings and walls. However, accumulation of porewater TCO₂ and dissolved organic carbon in sediments adjacent to burrows increased most rapidly in the presence of N. diversicolor, suggesting higher heterotrophic activity associated with this species. Surprisingly, bacterial abundance was lower around burrows of N. diversicolor than those from N. virens indicating that burrow environments from the first species harbour a more active bacterial community. Molecular fingerprints of the 16S rRNA gene from bacterial communities showed that the composition of the burrow linings and walls resembled the ambient anoxic sediment rather than the oxic sediment surface. On the other hand, the bacterial fingerprints of the sediment surrounding the burrows of the two polychaete species were markedly different suggesting either a site-specific difference in sediment parameters or a significant species-specific impact of the burrow inhabitants.